The aim of this work is to demonstrate the ability of atomic force mic
roscopy (AFM) to detect and to quantify specific immunological reactio
ns between antibodies and antigens, with a view to creating a very sen
sitive biosensor. A monolayer of antiferritin antibodies was adsorbed
onto alkyl silane modified silicon oxide substrates, which were charac
terized by X-ray photoelectron spectroscopy (XPS) and contact angle me
asurements. The sensitivity limit for antibody detection was quantifie
d by radioimmunoassay (RIA) and compared to that obtained by enzyme li
nked immune sorbent assay (ELISA) and by AFM after antibody binding wi
th colloidal gold labeled conjugates. In this latter case, substrate m
odification after reaction was checked by measuring the surface roughn
ess (R-rms) variations. AFM was found to be more sensitive than RIA, w
ith a detection limit of 0.3 x 10(-3) ng of antibodies per mm(2). Then
, the biosensor performance was investigated using ferritin solutions
of various concentrations: the antibody/antigen reaction was quantifie
d by directly detecting the antigen and measuring surface roughness mo
difications. Results were compared to sandwich immunoassay techniques.
Up to now, AFM has detected a minimum ferritin concentration of 0.06
mu g/mL.